feat(castle-siege): adopt the upstream Castle Siege data model and persistence

Brings in the database layer of upstream OpenMU PRs #754 and #860 without
touching AdaMu's working Castle Siege gameplay. This is purely additive: the
existing 5-phase implementation still runs exactly as before.

What is included:

- DataModel: CastleSiegeState (the original Season 6 values 0-9, which are
  exactly what the game client's CASTLESIEGE_STATE enum expects),
  CastleSiegeJoinSide, and the zone/NPC/upgrade definition types.
- Entities: CastleSiegeData, CastleSiegeGuildRegistration, CastleSiegeNpcState.
  These identify a guild by its persistent Guid rather than by name.
- Generated persistence: 8 BasicModel + 8 EntityFramework model classes,
  CastleSiegeExtensions, and the regenerated ExtendedTypeContext,
  MapsterConfigurator and GameConfiguration partials.
- Migrations: 20260730194321_AddCastleSiege and
  20260801162427_ConfigureCastleSiegePersistence, plus the model snapshot.
- EntityDataContext gains the two DbSets and the five model registrations.
- EntityFrameworkContextBase only publishes configuration changes for entities
  in the configuration schema, so siege state writes are no longer broadcast as
  configuration changes.

AdaMu-specific adaptations:

- UpdateVersion.AddCastleSiegeData is 105, not upstream's 100. AdaMu already
  ships 95-104, and the applied-update bookkeeping is keyed on this value, so a
  collision would skip or re-run updates on live databases.
- CastleSiegeInitializer does not seed a weekly StateSchedule. Upstream drives
  the cycle from a fixed Saturday schedule; AdaMu drives it manually from
  CastleSiegeEventPlugIn and the AdminPanel, so the schedule is left empty and
  nothing reads it.

The seeded NPC definitions match AdaMu's existing hard-coded coordinates
exactly (6 gates, the two crown switches and the crown), and additionally
provide 4 guardian statues, 6 guardsmen and real gate/statue hit point tables
that the current implementation does not have yet.

Two pre-existing migrations were restyled by upstream (copyright header, using
placement, trailing comma). No functional change.

Verified: full server build succeeds with 0 errors.

src/DataModel/Configuration/GameConfiguration.cs

@@ -300,6 +300,12 @@ public partial class GameConfiguration
     [MemberOfAggregate]
     public virtual ICollection<MiniGameDefinition> MiniGameDefinitions { get; protected set; } = null!;
 
+    /// <summary>
+    /// Gets or sets the castle siege configuration.
+    /// </summary>
+    [MemberOfAggregate]
+    public virtual CastleSiegeConfiguration? CastleSiegeConfiguration { get; set; }
+
     /// <inheritdoc />
     public override string ToString()
     {